Device for introducing a liquid substance into the exhaust gas of an internal combustion engine

ABSTRACT

A device for introducing a liquid reducing agent into the exhaust gas of an internal combustion engine includes an injection device and a retaining device. By means of the latter, the injection device is retained at least indirectly in the vicinity of an exhaust gas conduit and a cooling device cools the retaining device. An intermediate portion is disposed between the retaining device and the injection device, and this portion at least regionally influences the heat flow between the injection device and the retaining device.

The invention relates to a device for introducing a liquid substance into the exhaust gas of an internal combustion engine as generically defined by the preamble to claim 1. The subject of the invention is also a method for producing such a device.

German Patent Disclosure DE 103 24 482 A1 describes a device for injecting a liquid reducing agent into the exhaust gas of an internal combustion engine. To that end, the reducing agent is pumped from a storage container into a hollow retaining device, and from there back to the fuel tank. Via a branch fluidically downstream of the retaining device, reducing agent can be delivered to an injection device, which is retained by the retaining device. Because of the flow of reducing agent through the retaining device, the retaining device is cooled; that is, the retaining device includes a cooling device.

DISCLOSURE OF THE INVENTION

The object of the present invention is to refine a device for introducing a liquid substance into the exhaust gas of an internal combustion engine further in such a way that the liquid substance can be metered with high precision, and at the same time the service life of the device is improved.

This object is attained by a device having the characteristics of claim 1. Advantageous refinements are defined by dependent claims. A further means of attaining the object of the invention is disclosed by the coordinate claim, which pertains to a production method. Characteristics important to the invention are furthermore recited in the ensuing description and shown in the drawings, and the characteristics may be essential to the invention in quite various combinations.

By means of the device and method of the invention, a targeted influence on the heat transfer between the cooled retaining device and the injection device is made possible, specifically with the goal of both an improved heat transfer for cooling the retaining device and a reduced heat transfer for at least regionally avoiding heating of the injection device. The targeted and possibly even regional variation of the temperature of the injection device relieves the injection device, which leads to a longer service life. Particularly if the liquid substance is a reducing agent, then it does not age as much in the injection device, because of the lesser temperature stress. Since typical reducing agents in the injection device change to the vapor phase at a temperature of approximately 160° C., it is possible by the targeted variation of the temperature of the injection device to avoid boiling of the reducing agent in the injection device and the incorrect metering that would be associated with it.

This can be attained for instance by providing that between the relatively rigid injection device and the comparatively rigid retaining device, a less-rigid or even quite soft contact element is placed, which is deformed upon the mounting of the injection device on the retaining device. Since the contact element has a markedly lesser rigidity than the injection device and the retaining device, it is essentially only the contact element that is deformed, but not the injection device or the retaining device. Their function accordingly remains unimpaired. As a result of the deformation of the contact element, the contact element can press itself against, or in other words “conform” to, the injection device and the retaining element two-dimensionally and without play, creating an especially good thermal contact between the injection device and the contact element and between the contact element and the retaining device. Thus the contact element, because of its high thermal conductivity, can dissipate the heat, introduced into the injection device from the exhaust gas and the exhaust gas conduit, into the retaining device with good efficiency.

One material which can be deformed easily and plastically and which at the same time has excellent thermal conductivity is graphite.

Play-free deformation of the contact element with simultaneously only slight radial contact force can be attained if the contact element is annular, and if either the contact element or a contact region of the retaining element, oriented toward the contact element, has a slight conicity.

The cooling device preferably includes a cooling conduit, which is disposed in the retaining device and through which a coolant flows. As the coolant, reducing agent, coolant, or even fuel can be used. A cooling device of this kind is very effective and robust and at the same can be produced economically.

To minimize the heat input into the contact element and the retaining device, a thermal insulation means, such as a ceramic disk, should be disposed between the retaining device and the contact element, on the one hand, and the exhaust gas conduit, on the other.

A further possibility of influencing the heat transfer between the retaining device and the injection device is that the intermediate portion has a slight air gap. Air is a poor thermal conductor and makes a targeted regional reduction in the heat transfer possible. Furthermore, the air gap can be designed and dimensioned in such a way that the air located in it is comparatively cool, and already by this means alone, an unwanted heating of the injection device is reduced.

It is especially preferred if the slight air gap between the injection device and the retaining device is present in a region adjacent to the exhaust gas conduit. There, good insulation is especially important, to prevent a heat input from the retaining device, which in this region is heated especially strongly by the exhaust gas, into the injection device.

BRIEF DESCRIPTION OF THE DRAWINGS

An especially preferred exemplary embodiment of the present invention is described in further detail below, in conjunction with the accompanying drawings. In the drawings:

FIG. 1 is a schematic illustration of an internal combustion engine with a device for introducing a liquid reducing agent into the exhaust gas;

FIG. 2 is a more-detailed view of the device of FIG. 1, in a plane perpendicular to it; and

FIG. 3 is an enlarged view of an injection device and a first embodiment of a retaining device, with a contact element of the device of FIG. 1; and

FIG. 4 is a view similar to FIG. 3 of a second embodiment.

DESCRIPTION OF EMBODIMENTS

In FIG. 1, an internal combustion engine is identified overall by reference numeral 10. It includes combustion chambers 12, in which a fuel-air mixture is combusted. Hot combustion gases are removed from the combustion chambers 12 through an exhaust gas conduit 14. In it, there is an exhaust gas posttreatment system, in the form of an SCR catalytic converter 16. SCR stands for “Selective Catalytic Reduction”. In the SCR catalytic converter 16, the pollutant NOx is reduced, with the aid of liquid reducing agent, to N2 and H2O. An oxidation catalytic converter is typically located upstream of the SCR catalytic converter but is not shown in FIG. 1 for the sake of simplicity. Ammonia may be used as the reducing agent. For the sake of ease of handling, the ammonia is not metered into the exhaust gas in pure form but rather in the form of a precursor product. A urea-water solution can be considered in particular as the precursor product.

The engine 10 also includes a device 18, with which the reducing agent can be introduced into the exhaust gas flowing in the exhaust gas conduit 14. The device 18 described here is not, however, limited to the delivery of a urea-water solution but instead can be used generally in conjunction with other reducing agents as well. For instance, even fuel can be metered as a reducing agent into the exhaust gas. The invention can furthermore be used in combination with other exhaust gas posttreatment provisions and systems that have storage-type catalytic converters and/or particle filters.

The device 18 includes an injection device 20, such as an injector, which in a manner to be described in further detail hereinafter is retained directly on the exhaust gas conduit 14 by a retaining device 22. Through the injector 20, the reducing agent, which is identified in the drawings overall by reference numeral 24, finally reaches the exhaust gas conduit 14. As can be seen particularly from FIGS. 2 and 3, the retaining device 22 is annular, with a bottom plate 26 oriented toward the exhaust gas conduit 14, in which plate there is a through opening 28 through which an injection end 30 of the injector 20, pointing toward the exhaust gas conduit 14, is passed. A thermal insulation means 32 in the form of an annular disk, which is made for instance from plastic, is disposed between the bottom plate 26 and the exhaust gas conduit 14.

In a radially outer region, the bottom plate 26 is joined integrally to a hollow annular body 34 of overall rectangular cross section. The annular body 34 accordingly forms a radially outer region of the retaining device 22. The annular body 34 and bottom plate 26 are made from a comparatively rigid steel, as is the injector 20. A hollow chamber 36 in the annular body 34 forms an annular conduit with an inlet 38 and an outlet 40. The function of the annular conduit 36 will be addressed in further detail hereinafter.

Between the annular body 34 and the injector 20, there is an annular contact element 42. It is made from graphite and is retained in a slight press fit between the annular body 34 and the injector 20. The retaining device 22 also includes a cover plate 43, which represents the upper boundary, in FIGS. 2 and 3, of the retaining device 22. In the installed position shown in FIGS. 2 and 3, an inner jacket face 43 of the contact element 42 rests two-dimensionally on an outer jacket face 45 of the injector 20. An outer jacket face 46 of the contact element 42 rests two-dimensionally in the same way against an inner jacket face 48 of the annular body 34 of the retaining device 22. Because of the press fit, the contact element 42 is thus received without play between the injector 20 and the annular body 34 of the contact element 42. The two-dimensional and thus thermally optimal contact between the inner jacket face 44 and the outer jacket face 45, and between the outer jacket face 46 and the inner jacket face 48, is attained as a result of the comparatively low rigidity, compared to the injector 20 and the retaining device 22, of the contact element 42 made from graphite and as a result of the resultant good deformability.

As can be seen from FIG. 3, the outer jacket face 46 of the contact element 42 and the inner jacket face 48 of the annular body 34 are both embodied slightly conically, complementary to one another. As a result, the deformation of the contact element 42 and thus the attainment of a thermally optimal two-dimensional contact is promoted, while at the same time having an only slightly radial contact force of the contact element 42 against the outer jacket face 45 of the injector 20.

As can be seen from FIGS. 1 and 2, the reducing agent 24 is stored in a storage container 50. From this container, it is pumped to the inlet 38 of the annular conduit 36 via a pump 52. The outlet 40 of the annular conduit 36 communicates in turn with the storage container 50, via a return 54 and a heat exchanger 56. From the return 54, a feed line 58 branches off; it leads to the injector 20, and a metering valve 60 is disposed in it.

The operation of the engine 10 and of the device 18 for introducing the reducing agent 24 into the exhaust gas of the engine 10 is controlled and regulated by a control and regulating unit 62. To that end, the control and regulating unit 62 receives signals from various sensors, of which in FIGS. 1 and 2 only one is shown as an example, referred to by reference numeral 64. Among other things, the power of a drive motor 66, which drives the pump 52; the electromagnetic metering valve 60; and various control devices of the engine 10, such as injectors, with which the fuel is injected directly into the combustion chambers 12, are varied by the control and regulating unit 62.

The device 18 functions as follows: The reducing agent 24 is pumped by the pump 52 into the annular conduit 36 via the inlet 38. Since the reducing agent 24 coming from the storage container 50 is comparatively cold, it thus cools the annular body 34. Thus to this extent, the annular conduit 36 and the annular body 34 form a cooling device 68. Via the outlet 40 and the return 54, at least some of the reducing agent 24 that is heated in the cooling device 68 reaches the heat exchanger 56, where it is cooled down again before it returns to the storage container 50. As a function of the triggering of the electromagnetic metering valve 60, however, some of the reducing agent 24 flowing in the return 54 is carried via the feed line 58 to the injector 20 and is injected into the exhaust gas conduit 14.

Because of the heat of the exhaust gas flowing in the exhaust gas conduit 14, the exhaust gas conduit 14 itself also heats up. A transfer of this heat to the injector 20, however, is effectively reduced by the thermal insulation means 32. To that end, heat from the injector 20 is diverted by the contact element 42 into the annular body 34 and from there into the reducing agent 24, flowing into the annular conduit 36, that to this extent acts as a coolant.

The device 18 is produced such that upon the mounting of the injector 20 on the retaining device 22, the contact element 42 is deformed more markedly than the injector 20 and in such a way that it comes into contact two-dimensionally and without play with the injector 20 and the retaining device 22. It can also be seen from FIG. 3 that the through opening 28 in the bottom plate 26 of the retaining device 22 has a somewhat greater diameter than the injection end 30 of the injector 20. Between the bottom plate 26 and the injector 20 there is accordingly a gap 70, by which a heat input into the bottom plate 26 is reduced.

In the exemplary embodiment described above, the jacket face 46 of the contact element 42 and the jacket face 48 of the annular body 34 are embodied conically, complementary to one another. However, it is also possible for only of the two jacket faces to be conical, either that of the contact element 42 or that of the annular body 34.

A further embodiment of a retaining device is shown in FIG. 4. Here as below, those elements and regions which have equivalent functions to elements and regions described above have the same reference numerals and will not be described again in detail.

The embodiment of FIG. 4 does not have a contact element for improving the heat dissipation from the injector 20 into the retaining device 22; instead, it has a pronounced gap 70, which reduces a heat input from the retaining device 22 into the injector 20. The gap extends over the length of the entire injection end 30. Comparatively cool air is present in the gap 70. A thermal insulating means between the exhaust gas conduit 14 and the retaining device 22 can then optionally be dispensed with. 

1-10. (canceled)
 11. A device for introducing a liquid reducing agent into the exhaust gas of an internal combustion engine, the device comprising an injection device, a retaining device by which the injection device is retained at least indirectly in the vicinity of an exhaust gas conduit, and a cooling device which cools the retaining device, the cooling device including an intermediate heat transfer portion disposed between the retaining device and the injection device and at least regionally influencing the heat flow between the injection device and the retaining device.
 12. A device for introducing a liquid reducing agent into the exhaust gas of an internal combustion engine, the device comprising an injection device, a retaining device by which the injection device is retained at least indirectly in the vicinity of an exhaust gas conduit, a cooling device which cools the retaining device and the injection device, and an intermediate heat transfer element disposed between the retaining device and the injection device and at least regionally influencing the heat flow between the injection device and the retaining device.
 13. The device as defined by claim 12, wherein the intermediate portion includes a contact element disposed, in each case without play, between the injection device and a radially outer region of the retaining device, is in thermal communication with the injection device and the retaining device, in each case by two-dimensional contact, and is produced from a material with high thermal conductivity, and which at least in the contact regions with the injection device and/or the retaining device has a lesser rigidity than the injection device and/or the retaining device.
 14. The device as defined by claim 13, wherein the material of the contact element includes graphite.
 15. The device as defined by claim 13, wherein the contact element is annular, with a slight conicity in at least some regions.
 16. The device as defined by claim 14, wherein the contact element is annular, with a slight conicity in at least some regions.
 17. The device as defined by claim 13, wherein a contact region of the retaining element oriented toward the contact element has a slight conicity.
 18. The device as defined by claim 14, wherein a contact region of the retaining element oriented toward the contact element has a slight conicity.
 19. The device as defined by claim 11, wherein the cooling device comprises a cooling conduit disposed in the retaining device and through which a coolant flows.
 20. The device as defined by claim 12, wherein the cooling device comprises a cooling conduit disposed in the retaining device and through which a coolant flows.
 21. The device as defined by claim 13, wherein the cooling device comprises a cooling conduit disposed in the retaining device and through which a coolant flows.
 22. The device as defined by claim 14, wherein the cooling device comprises a cooling conduit disposed in the retaining device and through which a coolant flows.
 23. The device as defined by claim 11, further comprising thermal insulation means disposed between the retaining device and the contact element, on the one hand, and the exhaust gas conduit, on the other.
 24. The device as defined by claim 12, further comprising thermal insulation means disposed between the retaining device and the contact element, on the one hand, and the exhaust gas conduit, on the other.
 25. The device as defined by claim 13, further comprising thermal insulation means disposed between the retaining device and the contact element, on the one hand, and the exhaust gas conduit, on the other.
 26. The device as defined by claim 11, wherein the intermediate portion includes an air gap.
 27. The device as defined by claim 12, wherein the intermediate portion includes an air gap.
 28. The device as defined by claim 19, wherein the intermediate portion includes an air gap.
 29. The device as defined by claim 27, wherein the air gap between the injection device and the retaining device is present in a region adjacent to the exhaust gas conduit.
 30. A method for producing a device for introducing a liquid substance into the exhaust gas of an internal combustion engine, the device including a contact element that is a good thermal conductor disposed between a retaining device and an injection device, the method comprising deforming the contact element upon mounting of the injector on the retaining device, the contact element being deformed more markedly by the retaining device than by the injector and in such a way that it comes into contact two-dimensionally and without play with the injection device and the retaining device. 